Higher demands are often made today of machine-washed dishes than of dishes washed manually. After being washed in the dishwasher, a dish should be not only completely free of food residues, for example, but also free of whitish spots caused by water hardness or other mineral salts originating from dried drops of water in the absence of a wetting agent.
Modern automatic dishwashing agents meet these requirements through the integration of cleaning, care, water-softening and clear-rinse active ingredients and are known to the consumer as “2in1” or “3in1” dishwashing agents, for example. The automatic dishwashing agents provided for the private end user contain builders as the essential ingredient for the success of both cleaning and clear rinsing. These builders, first of all, increase the alkalinity of the cleaning liquor, wherein fats and oils are emulsified and saponified with an increase in alkalinity, and also reduce the water hardness of the cleaning liquor due to the chelating of the calcium ions contained in the aqueous liquor. The alkali metal phosphates have proven to be especially effective builders and for this reason form the main ingredient of by far the majority of commercially available automatic dishwashing agents.
Although phosphates are very valuable with regard to their advantageous effect as an ingredient of automatic dishwashing agents, their use is not without problems, however, from the standpoint of environmental protection, because a significant amount of the phosphate enters natural bodies of water via the household wastewater and plays a critical role, especially in standing bodies of water (lakes, ponds) when the latter are overfertilized. As a result of this phenomenon, which is also known as eutrophication, the use of pentasodium triphosphate in textile washing agents has been reduced substantially by law in some countries, e.g., United States, Canada, Italy, Sweden, Norway and/or completely banned in Switzerland. Since 1984, washing agents in Germany are allowed to contain at most 20% of this builder substance.
In addition to nitrilotriacetic acid, mainly sodium aluminosilicates (zeolites) are used as phosphate substitutes or replacements in textile washing agents. However, these substances are not suitable for use in automatic dishwashing agents for various reasons. Therefore, a number of substitutes are discussed in the literature as alternatives to alkali metal phosphates in automatic dishwashing agents, but the citrates are emphasized in particular.
Phosphate-free automatic dishwashing agents, which also contain carbonates, bleaches and enzymes in addition to a citrate, are described in European Patent EP 662 117 B1 (Henkel KGaA) and European Patent EP 692 020 B1 (Henkel KGaA), for example.
Another alternative to the alkali metal phosphates used as the only builder but preferably used in combination with citrates, is methyl glycine diacetic acid (MGDA). Automatic dishwashing agents that contain MGDA are described in European Patent EP 906 407 B1 (Reckitt Benckiser) or in European Patent Application EP 1 113 070 A2 (Reckitt Benckiser), for example.
Despite previous efforts, the manufacturers of automatic dishwashing agents have not so far succeeded in providing phosphate-free automatic dishwashing agents, which are comparable to or even exceed the phosphate-containing cleaning agents with regard to their cleaning and clear-rinse performance and in particular their residue-inhibiting performance. However, such equality in performance is a prerequisite for successful market introduction of cleaning agents that contain phosphate because by far the majority of end consumers will always decide against an ecologically advantageous product, despite broad public discussion, if this product does not meet the market standard with regard to its price and/or performance.
Accordingly, it is desirable to provide a phosphate-free automatic dishwashing agent which is comparable to or even exceeds traditional cleaning agents that contain phosphate with respect to its cleaning performance as well as with respect to its clear-rinse results and its performance with regard to inhibiting deposits. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.